Cloacin DF13

Cloacin DF13 is a type of Colicin, a bacteriocin made by E. coli which acts against other nearby E. coli to kill them with its 16s rRNase activity; it digests the 16s ribosomal subunit, ultimately leading to the death of the cell. It was initially discovered in Enterobacter cloacae, which gives it its name.

Synthesis and release
The operon encoding Cloacin DF13 is encoded on a plasmid in the producing cell. This operon also includes the Colicin Immunity Protein, and a protein to enable release of the cloacin to the surrounding area. The immunity protein binds to the cytotoxic domain of the cloacin to inhibit its 16s rRNase activity, and protect the producing cell.

Mechanism of uptake
The receptor binding domain binds to LutA, an outer membrane protein of the target cell that is constitutively expressed and parasitised by the cloacin. The translocation domain then recruits proteins from the Tol system to enable translocation across the membrane and in to the cytoplasm, through a mechanism as yet unidentified.

Receptor binding causes the dissociation of the immunity protein from the cytotoxic domain, allowing the rRNase activity to occur in the cytoplasm of the target cell.

Killing Activities
Cloacin DF13 kills its target cell with 16s rRNase activity. Its cytotoxic domain binds to and degrades the 16s subunit of the ribosome in the cell, preventing it from synthesising proteins. This ultimately leads to the death of the cell.